1. Field of Art
The present invention relates to a solid-liquid separator making use of activated carbon for separation of suspended matter in raw water in a water treatment process in a water purification plant.
2. Description of Relevant Art
Water purification plants employ various methods for water treatment in accordance with raw water as a treatment target. For some treatments of water containing, for instance, causative substances of foreign odor or taste (2-MIB, diosmin, etc), anion surfactants, phenols, trihalomethane or its precursor, volatile organochlorine compounds (trichloroethylene, etc), trace toxics (pesticides, etc) or the like, there has been use of activated carbon for adsorption of such substances.
FIG. 1 illustrates a water treatment system 100 for water purification plants as a general example making use of activated carbon. Raw water is drawn from a water source such as a river, and collected in a water intake well 1 near the water source. Raw water in the intake well 1 is transported to a water reservoir well 2 provided for temporary storage of incoming water, and is sent from there to a fast agitation basin 3.
The water treatment system 100 includes a facility 10 for adding activated carbon A to the intake well 1, as ‘a first activated carbon adding system’, and another facility 20 for adding activated carbon A to the reservoir well 2, as ‘a second activated carbon adding system’. Added activated carbon in the intake well 1, as well as that in the reservoir well 2, adsorbs thereon suspended matter in raw water. It is noted that the water treatment system 100 in FIG. 1 has two activated carbon adding systems being the first activated carbon adding system 10 for addition of activated carbon A to the intake well 1 and the second activated carbon adding system 20 for addition of activated carbon A to the reservoir well 2, and may simply have either the first activated carbon adding system 10 or the second activated carbon adding system 20.
There is a facility 12 for adding chemicals (i.e., flocculant) to the fast agitation basin 3, which is referred herein to ‘a first chemicals adding system’. The fast agitation basin 3 includes a first agitator 3a, which agitates raw water containing activated carbon A and flocculant, so that floc B is formed by an effect of flocculant. Raw water agitated in the fast agitation basin 3 is sent to a flocculation basin 4.
There is a facility 13 for adding chemicals (i.e., flocculation additive) to the flocculation basin 4, which is referred herein to ‘a second chemicals adding system’. The flocculation basin 4 includes a second agitator 4a, which agitates raw water by a slower speed than the first agitator 3a, so that floc B is grown larger by an effect of flocculation additive. Raw water agitated in the flocculation basin 4 and containing floc B is sent to a flocculating sedimentation basin 5.
At the flocculating sedimentation basin 5, sludge is settled out for separation with floc B inclusive, and dehydrated for condensation by a sludge condensing system 6, to dispose of as an industrial waste. As sludge is removed with floc B inclusive, resultant water is sent through a sand separator 7 for sand filtration and a chlorinator 8 for a chlorination process, to a distribution reservoir 9, where it is distributed to water stations.
The example in FIG. 1 is illustrated to add activated carbon to the intake well 1 and the reservoir well 2. There are two types of activated carbon for use in purification plants, being ‘granular activated carbon’ within a range of approximately 150 μm or more in particle size and ‘powdery activated carbon’ within a range under approximately 150 μm in particle size, having their applications different from each other as well as particle sizes.
Generally, ‘granular activated carbon’ is applied to a subsequent stage of sand filtration, and used for collection of organic compounds, and coloring components of low molecular weights in a molecular weight range under approximately 1500 that have not been removed by flocculating sedimentation.
Granular activated carbon undergoes development of a breakthrough (as an equilibrant between adsorption rate and desorption rate balanced with each other failing to work for adsorption) along with adsorption of organic compounds. The development of breakthrough has an increased rate, in particular with adsorption of organochlorine compounds. Granular activated carbon thus has a reduced adsorption capacity in due course. However, there are treatments available for regeneration of adsorption capacity. Although available treatments for regeneration of adsorption capacity need a dedicated contact basin, water treatment processes may well have such a regeneration treatment incorporated therein to implement an efficient recycling in a long-term use of activated carbon.
As an available method for regeneration of adsorption capacity of activated carbon, there is a ‘water vapor activation method’ using water vapor at hot temperatures about 900° C. for the activation, and a ‘chemicals activation method’ using chemicals such as zinc chloride or sulfuric acid for a woody material to be dipped therein before carbonization. The chemicals activation method may cause an elution of chemicals or heavy metals such as zinc into water under treatment, and it generally is unused for activation of carbon for water purification, giving place to the water vapor activation method.
On the other hand, in general, ‘powdery activated carbon’ is added in processes before flocculating sedimentation such as of drawn water or incoming water, as illustrated in FIG. 1, for use to adsorb and remove suspended matter, against a temporary declination in quality of taken water, such as generation of odor in drought period or summer season, or overgrowth of phytoplankton called algal bloom. This is because incorporation of suspended matter such as algae into flock would makes this lighter in specific gravity, prone to breakage, and debased in sedimentation property, needing a great deal of flocculant to be input with an increased cost for chemicals, and declination in quality of taken water should be coped with by use of activated carbon for removal of suspended matter in processes before flocculating sedimentation, allowing for an enhanced performance with a decreased running cost on flocculant.
Instead, if powdery activated carbon is input, there might be increased quantities of flocculant and flocculation additive added with an increased cost for chemicals, as well as with an increased rate in production of sludge constituting difficulties in treatments for disposal and collection. In addition, powdery activated carbon is very small in particle size, which constitutes a bar to a treatment for regeneration of adsorption capacity. Accordingly, powdery activated carbon is employed typically as a countermeasure, not for regular use, but for temporary irregular use.
Besides the use of traditional sedimentation for coagulate settling methods, there is a use of centrifugal force for liquid cyclones as a solid-liquid separator employable in water purification. Liquid cyclones are adapted to make use of centrifugal forces produced by swirling momentum of incoming liquid, for solid-liquid separation due to a difference in specific gravity between solid and liquid. Accordingly, liquid cyclones have a motion-less structure that can be implemented by a simple configuration with an enhanced performance per occupied floor area, as an advantage.
As one of techniques employing a liquid cyclone and activated carbon in combination for treatments in water purification, there is a technique disclosed in Japanese Patent Application Laid-Open Publication No. 2005-13892 (referred herein to JP 2005-13892 A), which included a process of regenerating used granular activated carbon to re-input to, among others, a fast agitation tank and a mixing tank. In the technique disclosed in JP 2005-13892 A, granular activated carbon was regenerated to adsorb suspended matter, and provide a promoter effect to promote floc settling with an increased floc settling rate. Regeneration of activated carbon was followed by reuse, with a resultant reduction in waste amount of activated carbon.
However, in the technique disclosed in JP 2005-13892 A, granular activated carbon was input in a treatment process before flocculating sedimentation, so that flocculant was added to raw water containing granular activated carbon, resulting in an increased amount of chemicals such as flocculant required for flocculating sedimentation, as an issue. Further, in the technique disclosed in JP 2005-13892 A, granular activated carbon was contained in floc settled in a sedimentation basin, as part thereof to be wasted together with the rest, resulting in production of a plenty of sludge difficult to waste, as an issue.
In view of the foregoing issues, the present invention provides a solid-liquid separator allowing for a reduced amount of chemicals to be used, with production of a reduced amount of sludge.